1. Field of the Invention
The present invention relates to an anisotropically conductive sheet suitable for use, for example, in electrical connection between circuit devices such as electronic parts, or as a connector in inspection apparatus for circuit devices such as printed circuit boards and semiconductor integrated circuits, to a production process thereof, and to applied products thereof.
2. Description of the Background Art
An anisotropically conductive sheet is a sheet exhibiting conductivity only in its thickness-wise direction or having pressure-sensitive conductive conductor parts exhibiting conductivity only in its thickness-wise direction when pressurized in the thickness-wise direction. Since the anisotropically conductive sheet has features that compact electrical connection can be achieved without using any means such as soldering or mechanical fitting, and that soft connection is feasible with mechanical shock or strain absorbed therein, it is widely used as a connector for achieving electrical connection of a circuit device, such as a printed circuit board with a leadless chip carrier, liquid crystal panel or the like in fields of, for example, electronic computers, electronic digital clocks, electronic cameras and computer key boards.
On the other hand, in electrical inspection of circuit devices such as printed circuit boards or semiconductor integrated circuits, it is conducted to cause an anisotropically conductive sheet to intervene between an electrode region to be inspected of a circuit device, which is an inspection target, and an electrode region for inspection of a circuit board for inspection in order to achieve electrical connection between electrodes to be inspected formed on one surface of the circuit device to be inspected and electrodes for inspection formed on the surface of the circuit board for inspection.
As such anisotropically conductive sheets, there have heretofore been known those of various structures. For example, Japanese Patent Application Laid-Open No. 93393/1976 discloses anisotropically conductive sheets obtained by uniformly dispersing metal particles in an elastomer, and Japanese Patent Application Laid-Open No. 147772/1978 discloses anisotropically conductive sheets obtained by unevenly distributing particles of a conductive magnetic material in an elastomer to form many conductive path-forming parts extending in the thickness-wise direction thereof and insulating parts for mutually insulating them. Further, Japanese Patent Application Laid-Open No. 250906/1986 discloses anisotropically conductive sheets with a difference in level defined between the surface of conductive path-forming parts and insulating parts.
As illustrated in FIG. 17, in these anisotropically conductive sheets, conductive particles P are contained in a base material composed of an elastic polymeric substance E in a state oriented so as to align in the thickness-wise direction of each sheet to form a chain C, and adhered integrally to the elastic polymeric substance E.
However, the conventional anisotropically conductive sheets involve the following problems.
In electrical inspection of a circuit device, as illustrated in FIG. 18, an electrode 91 to be inspected of the circuit device (hereinafter may also be referred to as xe2x80x9cthe circuit device to be inspectedxe2x80x9d) 90, which is an inspection target, is brought into contact with a surface of the anisotropically conductive sheet, for example, an end surface of a conductive path-forming part while an electrode 96 for inspection of a circuit board 95 for inspection is brought into contact with another surface of the anisotropically conductive sheet, for example another and surface of the conduct path-forming part, and the anisotropically conductive sheet is pressurized in the thickness-wise direction thereof, thereby achieving electrical connection between the electrode 91 to be inspected of the circuit device 90 to be inspected and the electrode 96 for inspection of the circuit board 95 for inspection.
In this state, the anisotropically conductive sheet is held between and pressurized by the electrode to be inspected of the circuit device to be inspected and the electrode for inspection of the circuit board for inspection, whereby the elastic polymeric substance E making up the base material is compressed in the thickness-wise direction to be deformed, and moreover the conductive particles P are moved, and so the chain C thereof is changed from the linear form extending in the thickness-wise direction to a complicated form, and a portion about the conductive particles P in the elastic polymeric substance E is deformed into a complicated form with the movement of the conductive particles P, since the elastic polymeric substance E and the conductive particles P adhere integrally to each other.
As described above, in the conventional anisotropically conductive sheets, not only compressive force in the thickness-wise direction, but also complicated and considerably great stress caused by the movement of the conductive particles is applied to the portion about the conductive particles P in the elastic polymeric substance E making up the base material at every time the sheet is held pressurized in the thickness-wise direction thereof. Therefore, the portion about the conductive particles P in the elastic polymeric substance E is deteriorated when the sheet is used repeatedly. As a result, an electrical resistance of the sheet in the thickness-wise direction is increased, and so the required conductivity cannot be retained to fail to achieve long service life.
In the electrical inspection of circuit devices such as semiconductor integrated circuits and printed circuit boards, tests under a high-temperature environment, such as a burn-in test and a heat cycle test are conducted for the purpose of developing latent defects of such a circuit device. Since the coefficient of thermal expansion of the elastic polymeric substance E making up the base material of the anisotropically conductive sheet is great, the elastic polymeric substance intends to expand when it is exposed to a high-temperature environment. Therefore, when the temperature about the anisotropically conductive sheet is raised in the state that the anisotropically conductive sheet has been held pressurized in the thickness-wise direction thereof, i.e., the state that the portion about the conductive particles P in the elastic polymeric substance E making up the base material has been deformed into a complicated form, greater stress is applied to the portion about the conductive particles P in the elastic polymeric substance E, and so the portion about the conductive particles P in the elastic polymeric substance E is prematurely deteriorated when such a test under the high-temperature environment is conducted repeatedly. As a result, the required conductivity cannot be retained to more shorten the service life.
The present invention has been made on the basis of the foregoing circumstances and the first object thereof is to provide of an anisotropically conductive sheet capable of retaining the required conductivity over a long period of time even when it is used repeatedly over many times, or even when it is used under a high-temperature environment, and thus achieving a long service life owing to its high durability upon repeated use and thermal durability.
The second object of the present invention is to provide a process for producing an anisotropically conductive sheet capable of achieving a long service life owing to its high durability upon repeated use and thermal durability.
The third object of the present invention is to provide an adapter for inspection of circuit devices, which is equipped with an anisotropically conductive sheet capable of achieving a long service life owing to its high durability upon repeated use and thermal durability and permits executing inspection of a circuit device with high efficiency and stably retaining a good electrically connected state even at varied temperatures.
The fourth object of the present invention is to provide an inspection apparatus for circuit devices, which is equipped with an anisotropically conductive sheet capable of achieving a long service life owing to its high durability upon repeated use and thermal durability and permits executing inspection of a circuit device with high efficiency.
The fifth object of the present invention is to provide an electronic part-packaged structure which permits stably retaining a good electrically connected state over a long period of time.
According to the present invention, there is provided an anisotropically conductive sheet containing conductive particles exhibiting magnetism in a state oriented in a thickness-wise direction of the sheet in an elastic polymeric substance, wherein the durometer hardness of the elastic polymeric substance is 20 to 90, and a lubricant or parting agent is coated on the surfaces of the conductive particles.
In the anisotropically conductive sheet according to the present invention, the amount of the lubricant or parting agent coated on the surfaces of the conductive particles may preferably be 10/Dn to 150/Dn parts by mass per 100 parts by mass of the conductive particles, wherein Dn means the number average diameter (xcexcm) of the conductive particles.
In the anisotropically conductive sheet according to the present invention, the lubricant or parting agent coated on the surfaces of the conductive particles may preferably be that containing silicone oil.
In the anisotropically conductive sheet described above, the silicone oil may preferably contain fluorine atom(s) in its molecule.
In the anisotropically conductive sheet according to the present invention, the lubricant or parting agent applied to the surfaces of the conductive particles may preferably be a fluorine-containing lubricant or parting agent.
The anisotropically conductive sheet according to the present invention may preferably comprise a plurality of conductive path-forming parts each closely containing the conductive particles and extending in the thickness-wise direction of the sheet, and insulating part(s) for insulating these conductive path-forming parts mutually.
According to the present invention, there is also provided a process for producing an anisotropically conductive sheet, which comprises the steps of coating the surfaces of conductive particles exhibiting magnetism with a lubricant or parting agent, forming a sheet-forming material layer with the conductive particles coated with the lubricant or parting agent dispersed in a liquid material for the elastic polymeric substance, which will become an elastic polymeric substance by a curing treatment, applying a magnetic field to the sheet-forming material layer in the thickness-wise direction thereof, and subjecting the sheet-forming material layer to the curing treatment.
According to the present invention, there is further provided an adapter for inspection of circuit devices, comprising a circuit board for inspection on the surface of which a plurality of electrodes for inspection has been formed in accordance with a pattern corresponding to electrodes to be inspected of a circuit device to be inspected, and the above-described anisotropically conductive sheet integrally provided on a surface of the circuit board for inspection.
In the adapter according to the present invention, at least a part of each of the electrodes for inspection in the circuit board for inspection may preferably be formed of a magnetic material.
According to the present invention, there is still further provided an inspection apparatus for circuit devices, comprising a circuit board for inspection on the surface of which a plurality of electrodes for inspection are formed in accordance with a pattern corresponding to electrodes to be inspected of a circuit device to be inspected, and the above-described anisotropically conductive sheet interposed between the circuit board for inspection and the circuit device.
According to the present invention, there is yet still further provided an electronic part-packaged structure comprising a circuit board and an electronic part electrically connected to the circuit board through the above-described anisotropically conductive sheet.
According to the anisotropically conductive sheet of the present invention, the lubricant or parting agent is applied to the surfaces of the conductive particles, whereby the lubricant or parting agent is interposed between the conductive particles and the elastic polymeric substance making up the base material, and so the conductive particles and the elastic polymeric substance are prevented from adhering integrally to each other and become a state that they can be slidably moved. Accordingly, the portion about the conductive particles in the elastic polymeric substance is prevented from being deformed into the complicated form with the movement of the conductive particles when the sheet is held pressurized in the thickness-wise direction thereof, whereby the stress to be applied to the portion about the conductive particles is relaxed, so that the required conductivity of the sheet is retained over a long period of time even when the sheet is used repeatedly, or it is used under a high-temperature environment.